To be honest you're better off looking for a boxing school if you ask me. If you can find a quality kick boxing club, that's a decent choice as well. There are a few variations of karate that are actually effective styles. Kyokushin Karate is a very straight forward style where you'll probably find yourself actually sparring with partners. You'll spend some time learning Kata(don't know where I stand on this) but you'll probably have a lot of fun with the bag work, as well as learning some pretty effective technique. You should probably stay away from Tae-Kwon-Do. General concencus seems to be that it's a joke in comparison to some other styles of standup. Muay Thai for example.